This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present techniques. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Any of a number of subsea separation techniques may be used to enhance the amount of oil and gas recovered from subsea wells. However, subsea separation at water depths greater than 1500 meters becomes especially challenging due to the environmental conditions. As water depth increases, the external pressure on a vessel created by the hydrostatic head increases the required wall thickness for vessels used for subsea processing. At water depths greater than 1500 meters, this wall thickness has increased to such an extent that typical gravity separation is not practical. In addition, vessels with such a large wall thickness can be a challenge to fabricate, and the added material and weight can impact project economics, as well as the availability of the vessel for maintenance. As a result, large diameter separators often cannot be used at such depths.
Further information may be found in U.S. Pat. No. 8,282,711 B2 (the '711 patent). This patent relates to subsea installation and a method for separation of liquid and gas. This disclosure is directed toward separation of liquids and gases from a subsea production fluid, using a pipe system that splits the flows of the liquid and gaseous fluids.
However, the '711 patent does not disclose separating individual oil and water streams from a mixed phase oil/water flow of fluid. Furthermore, this reference does not provide a method for sand separation or the prevention of sand deposition in the pipe separator. The reference also does not provide for polishing of the gas or the water streams such that either could be re-injected.
Additional information may also be found in U.S. Pat. No. 7,490,671 B2. This patent relates to a pipe separator with improved separation of oil gas and water. This system utilizes cyclonic separation for gas-liquid separation followed by oil-water separation in a pipe separator that must be aided by electrostatic coalescence.
Further information may also be found in U.S. Pat. No. 7,516,794 B2. This system is similar to that in U.S. Pat. No. 7,490,671 B2, however, with a new requirement of being “piggable”.
Additional information may also be found in U.S. Application 2008/0116072 A1. This system utilizes an electrostatic coalescer to treat an oil or emulsion stream which is extracted from an oil-water separator and returned to the same separator. It provides multiple arrangements of separators in which the technology described herein can be applied.
None of the references cited above include a control volume or a polishing section that is used to regulate the outlet of each line, thereby flowing a substantially oil stream, a substantially water stream and an oil/water emulsion.